1. Field of the Invention
The present invention relates to an optical recording and playback apparatus, and more particularly, to a pre-pit signal generator, a semiconductor integrated circuit, and a pre-pit signal generation method.
2. Description of the Related Art
As an optical recording media, a recordable digital versatile disc (DVD-R) and a rewritable digital versatile disc (DVD-RW) are known. An optical recording and playback apparatus generates record marks on a groove track during recording, and reads the record marks during playback. When information is recorded to or played back from such an optical recording medium, a pre-pit signal generator detects a land pre-pit on the optical recording medium as position information by use of reflected light of a recording beam irradiated onto the optical recording medium.
The optical recording and playback apparatus detecting a radial upper signal and a radial lower signal bisected in a tangential direction of a recording track on the optical recording medium is known. The pre-pit signal generator provides a radial push-pull signal obtained by subtracting the radial lower signal from the radial upper signal (hereinafter referred to as a “first related art”).
However, in the pre-pit signal generator according to the first prior art, amount of a reflected light of the land pre-pit is reduced when record mark portions and the land pre-pits on the optical recording medium become adjacent to each other. If the amount of the reflected light is reduced, then a binarizable range of a radial push-pull signal is narrowed. Moreover, because information components of an adjacent track leak to the radial push-pull signal, there has been a problem that the signal becomes unbalanced due to tracking errors of information reading spots.
To solve the above-described problem, the pre-pit signal generator using the radial upper signal amplified by k1 and the radial lower signal amplified by k2 (hereinafter referred to as a “second related art”) has been proposed. (refer to Japanese Patent Application Laid-open 2001-23168). The pre-pit signal generator generates radial push-pull signal obtained by subtracting the radial lower signals amplified by k2 from the radial upper signals amplified by k1. If the gain k1 is set larger than the gain k2, the binarizable range of the radial push-pull signals is expanded.
However, the pre-pit signal generator disclosed in the second related art unbalances an amplification ratio of the radial upper signals to the radial lower signals. The unbalance of the amplification ratio leaves in-phase components to be canceled on subtraction in the radial push-pull signals. High-frequency noise included in the radial push-pull signals becomes louder. The land pre-pit detection performance of the pre-pit signal generator is improved when there are record marks in the groove track adjacent to the land pre-pits. Specifically, there is a problem that the land pre-pit detection performance is deteriorated when there are no record marks.